Aspirin alone a good clot buster after knee surgery -- ScienceDailyOver three months, just 1.16 percent of aspirin patients developed a serious blood clot. That was true for 1.42 percent of anticoagulant patients, according to the Michigan study. This was not statistically different. So, neither drug appeared better than the other -- but aspirin has some obvious advantages. "Aspirin is easy to take and much less expensive," Hallstrom says. "Patients can get it over the counter for pennies, while the other anticoagulants require monitoring, injections, frequent dose adjustments and are extremely expensive." The reported cost for a 30-day supply of rivaroxaban is approximately $379 to $450; heparin is estimated at $450 to $890. Although warfarin costs a few dollars for a 30-day supply, its cost approaches that of the other anticoagulants when doctor visits for monitoring are factored in, Hallstrom says.